This invention relates generally to screw cutting lathes and more particularly to a vibration threading lathe for cutting precision screw threads which is capable of cutting screw threads with excellent machining efficiency on difficult-to-cut materials such as stainless steel, titanium, and beryllium copper by vibration threading wherein a pulsive cutting force waveform is utilized.
In the case of machining screw threads with a cutting tool on the surface of a difficult-to-cut material such as stainless steel, titanium, or beryllium copper such as, for example, a stainless-steel material of cylindrical shape of an outer diameter of 10 mm or less and a thin wall of 0.5 mm or less, according to known machining practice, the cutting tip of the cutting tool will be worn after machining a number of workpieces on the order of 40 to 50 pieces, and it will be necessary to replace the cutting tip. Furthermore, in order to finish to specific dimensions, 7 to 8 cuts will be required. Thus, such a machining operation has heretofore been inefficient.
In general, furthermore, even under machining conditions by which machining of screw threads is possible with a single cut, it has heretofore been necessary always to carry out a finish cut of the order to at least zero to a number of tens of microns after rough machining for reasons such as dimensional stability and shape precision.
Still another difficulty is that, in ordinary conventional machining in the case where, for example, screw threads of M=30 and P=1.5 are formed with a single cut on stainless steel, the principal force component of the resistance to cutting is of a great magnitude e.g. approximately 230 kg. In order to withstand this large resistance, the driving mechanisms of the cross slide holding the cutting tool and the longitudinal feed carriage or saddle as well as the tool rest or mechanism fixing the cutting tool must be made to have high strength and rigidity. As a consequence, the related structural parts or the entire machine must unavoidably be made bulky and strong.